Hobbsy,
I don't mean to offend you but you are wrong.Dave Gierke can explain it better than me but I will try.
Okay,assume you have an engine that vibrates more than it should because the counterbalance on the crankshaft is not heavy enough.[common problem on older engines]
This is what you do,
1 make sure piston is at top dead center
2 put on a unbalanced prop, heavy blade down

That is it ,pretty simple.